Vacuum Rectifiers and SS Diode Emulators

[Helmholtz]

FWIW,
This same JTM50 puts out 47W to 49W with the mains selector at 220V, DC current around 260mA.
Earlier data was with selector at 240V.
Average mains voltage over here is 226V to 228V.

[Merlinb]

whenever I try to do anything based on measurements... will lead to a trail of comments about "well, those are just replacements; the REAL XYZ126325 transformers used in Fender/Marshall/vox/boutique#1 are made with plutonium dioxide and have more/better [something or other].

Counterpoint: People who think the spirit of Henrix lies in what colour wire was originally used, probably aren't the core audience for your technical articles.

[Tom Phillips]

Counterpoint: People who think the spirit of Henrix lies in what colour wire was originally used, probably aren't the core audience for your technical articles.

Speaking of such talent as Hendrix.
I have a good friend who was a member of an opening band for a Hendrix show. He actually shared a dressing room with Hendrix at least once. My friend told me that Hendrix was warming up in the dressing room using a small solid state student type amp and he still sounded like Jimi Hendrix. Jimi was also changing the strings on his own guitar. The stage setups and the tour amenities were very simple in those days of 1967.

[g1]

Jimi was also changing the strings on his own guitar. The stage setups and the tour amenities were very simple in those days of 1967.

I often imagine him going to the drugstore to test tubes and pick up replacements. And I think he would either laugh or give a puzzled expression when asked about how he set his bias.

[Merlinb]

I hate to ask, but would it be possible for you to add to that batch of measurements the primary winding resistances and maybe, if you can, the actual DC current into the CT of the output transformer under no-signal idle and full(ish) power output? It's a big ask, I know, @ others: Anybody got time to measure transformers similar to what Tom has done?

A '50W' circuit I have tested, showing the change in PA currents and B+ voltage as the signal into the phase inverter is increased.

[R.G.]

Thank you Merlin. That's a great set of info.
R.G. runs off to the simulator...

[Tom Phillips]

A '50W' circuit I have tested, showing the change in PA currents and B+ voltage as the signal into the phase inverter is increased.

Nice!. This discussion thread has brought a lot of interesting information to light.

[Helmholtz]

A '50W' circuit I have tested, showing the change in PA currents and B+ voltage as the signal into the phase inverter is increased.

This is a rather stiff power supply. B+ sag is less than 30V between idle and full power.
(My JTM50 with GZ34 and EL34s sags by 52V between idle and 47W output. B+ at idle is 452V, so comparable.)
As the HT winding resistance looks quite low I'm wondering if you used a toroidal PT?

[loudthud]

When you say Full Power, do you mean output just below clipping, or full Rail to Rail Square Wave ?

[Helmholtz]

When you say Full Power, do you mean output just below clipping, or full Rail to Rail Square Wave ?

With "full power" I always mean just before clipping.
Power measurements with clipping are not really comparable.

[Merlinb]

This is a rather stiff power supply. B+ sag is less than 30V between idle and full power.
(My JTM50 with GZ34 and EL34s sags by 52V between idle and 47W output. B+ at idle is 452V, so comparable.)

Makes sense, adding a GZ34 to my PSU would roughly double the impedance, so roughly double the sag.

As the HT winding resistance looks quite low I'm wondering if you used a toroidal PT?

No it was one of these:
https://modulusamplification.com/50w...004-3199-p.asp